Gangliosides are sialic acid-containing glycosphingolipids highly enriched in the vertebrate nervous system. Although their functions have not been fully clarified, they are thought to mediate neural cell-cell recognition and modulate intracellular signaling [1]. Gangliosides are implicated in various neural disorders, primarily the autoimmune neuropathies, but also in storage disorders, e.g. Tay-Sachs disease or Sandhoff disease [2-4]. High-affinity IgG anti-ganglioside antibodies may be used to develop animal models of autoimmune neuropathies and probe normal ganglioside functions. However, it has been difficult to produce high-affinity IgG antibodies against major brain gangliosides, especially GM1, GD1a, and GT1b [5]. This unresponsiveness has been attributed to poor immunogenicity, T-cell independence, and tolerance [5-7]. Advances in genetics provide a potential solution to this problem. Several studies have shown that mice genetically engineered to lack the glycosyltransferase gene for ganglioside synthesis do not express complex gangliosides [8-12]. These mice, immunologically naive to complex gangliosides, have been used for raising new antibodies against complex gangliosides[2, 6, 13, 14].
The Lc3-synthase gene (β1,3-N-acetylglucosaminyltransferase-V: β3Gn-T5) enzyme initiates the formation of the lacto-/neolacto-series ganglioside by transferring GlcNAc in a β1,3-linkage to lactosylceramide (FIG. 1A) [15]. The β3Gn-T5 is detected in mouse development and then again later mainly in the spleen and placenta in adult mice. Additionally, Lc3-synthase transcripts are found in cerebellar Purkinje cells of the adult mouse brain. On the other hand, lacto-series gangliosides such as 3′-isoLM1 and 3′,6′-isoLD1 have been reported to be major mono- and oligo-sialogangliosides, respectively, of human gliomas [16-18]. In those studies, monoclonal antibodies (mAbs) such as SL-50, DMab-14, or DMab-22 recognizing lacto-series gangliosides were successfully produced; however, those antibodies proved to be of the low-affinity IgM subclass.
There is a continuing need in the art to obtain high-specificity and high-affinity reagents for treating tumors, especially brain tumors.